The D.C. public school system has hired 1,100 new teachers and has only 35 vacancies left to fill before classes start Monday, Superintendent Arlene Ackerman said yesterday, just before welcoming thousands of educators at a "Back to School" rally.

About 350 of the city's 5,100 teachers are not certified, down from 1,200 a year ago.

Attendance at the upbeat rally--dubbed "Reaching Higher: On the Road to Exemplary Achievement"--at MCI Center was mandatory for D.C. teachers on their first day back at work.

But the audience in the cavernous arena appeared far smaller than the 7,000 teachers, administrators and aides who were expected, and several teachers said a number of their colleagues had not come.

"Your jobs are the most important jobs in the city," D.C. Council member Kevin P. Chavous (D-Ward 7) told the teachers. "Let's not give up on any child, no matter how difficult the circumstances are."

Superintendent Arlene Ackerman asked teachers to remind themselves "each day of the incredible opportunity we have to tap the unlimited potential of our students."

Diane Johnson, a 19-year veteran who teaches at Kenilworth Elementary School in Northeast Washington, said the rally added to her excitement about the school year.

But Seung Lee, 24, a newly hired English as a second language teacher at Lincoln Middle School in Northwest Washington, called the gathering "pretty much a waste of time. There are other things we could be doing in the classroom that would be better."

Speakers at the rally included Mayor Anthony A. Williams (D); Del. Eleanor Holmes Norton (D-D.C.); financial control board Vice Chairman Constance B. Newman; Chavous, chairman of the council's education committee; school board Vice President Dwight E. Singleton (Ward 4); schools trustee board Chairman Maudine R. Cooper; and Washington Teachers' Union President Barbara Bullock.

At a news conference before the rally, Ackerman said the school system needs time to rebuild. "In five years, you are going to see a District you are really proud of," she said.

The rally itself was a swirl of pride and politics.

Newman and other speakers took pains to praise Ackerman, who has angered some parents, advocates and elected officials in her two-year effort to overhaul the troubled school system.

Ackerman showed a videotape documenting the evolution of D.C. schools from the 19th century until today.

Images of children sitting in front of computers were interspersed with headings such as "Hope" and "Dream makers."

The award-winning show choir from the Duke Ellington School of the Arts performed, as did champion cheerleading squads from Dunbar High School and Winston Educational Center, and the Anacostia High School marching band.

The teachers cheered loudest for the student performers--and for the announcement that they will receive long-awaited retroactive pay raises next week.

Applause also echoed off the center's towering ceiling when teachers were told that they could pick up $150 vouchers for school supplies--a welcome new initiative in a school district where teachers routinely dip into their own pockets to buy paper and other basics.

Newcomers from the national Teach for America program sported fresh haircuts and lots of optimism.

"I think there is a perception that D.C. schools are bad. I don't think that's true," said Ben Bruce, 22, a District native who attended private schools but will teach science at Jefferson Junior High School in Southwest. "I think my school is great."

Teachers headed to their classrooms or training sessions as the rally stretched 30 minutes past the scheduled noon closing.

Some said they felt slightly drained from sitting in their seats since 9 a.m.

"It was a little long," said Geneva Greene, who will teach at C.W. Harris Elementary School in Southeast. "I would have preferred to have prep time in the classroom, but I enjoyed it. It's good to do things like this."

CAPTION: Anela Chamblee, a reading specialist at Calvin Coolidge High School, listens to a speaker at the "Back to School" rally at MCI Center.

CAPTION: Members of the Woodson Senior High Junior ROTC post the colors as the rally begins.